1. Field of the Invention
This invention relates to non-destructive testing, and more particularly to the non-destructive testing of sheet materials such as steel plate.
Non-destructive testing is one of the standard techniques for testing the quality of products and materials, and amongst the most common non-destructive testing techniques are ultrasonic testing techniques. Ultrasonic techniques may be used for detecting surface defects and/or internal defects and/or thickness variations.
Non-destructive testing of steel in sheet form such as steel plate (which may for example be of the order of 3 mm in thickness or greater) is a particularly important application of the technique, because such steel plate is the end product of the relevant steel production process, and the provision of testing on an automatic basis of the quality of the plate produced is of great utility to the manufacturer.
2. Description of the Prior Art
Known and existing methods of such automatic ultrasonic testing of sheet materials usually involves moving one or more testing heads in a straight line along the length of the material, although in an attempt to cover a greater area of the sheet material a sinusoidal path of the testing head or heads relative to a sheet of material has been proposed and used in some instances by transverse oscillation of the head as the sheet material moves therepast. A continuing problem with these previous proposals and existing methods is the limitation of coverage of the testing across the sheet material.